A test of different rotational Raman linewidth models: Accuracy of rotational coherent anti-Stokes Raman scattering thermometry in nitrogen from 295 to 1850 K

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Abstract
Rotational Raman linewidths calculated from three different models have been used in temperature measurements by rotational coherent anti‐Stokes Raman scattering (CARS)—a semiclassical ab initio model, the modified exponential energy gap model (MEG), and the energy corrected sudden scaling law (ECS). Experimental rotational CARS spectra were generated, using the dual‐broadband approach, in pure nitrogen at atmospheric pressure in a heat pipe in the temperature range from 295 to 1850 K. Below 1500 K, the temperatures evaluated using the ECS linewidths agreed with the heat‐pipe temperatures to within 20 K. Above 1500 K, the errors in the evaluated temperatures increased steeply for all linewidth models, reaching errors of several hundreds of Kelvins at 1850 K. This behavior of the evaluated temperature is probably caused by the uncertainty in the values of the rotational Raman linewidths for high rotational states at high temperatures. This work therefore illustrates that rotational CARS can be used for experimentally studying Raman linewidths and in particular their dependence on temperature and rotational quantum number. The influence of different experimental parameters on the evaluated temperatures is discussed, and the spectral synthesis program is presented.